Thin film deposition techniques are widely used to build interconnects, plugs, gates, capacitors, transistors and other microfeatures in the manufacturing of microelectronic devices. Thin film deposition techniques are continually improved to meet the ever increasing demands of the industry because microfeature sizes are constantly decreasing and the number of microfeature layers is constantly increasing. As a result, the density of components and the aspect ratios of depressions (e.g., the ratio of the depth to the size of the opening) are increasing. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms, and corners in deep depressions that have very small openings.
One widely used thin film deposition technique is chemical vapor deposition (CVD). In a CVD system, one or more reactive precursors are mixed in a gas or vapor state and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes a reaction between the precursors to form a solid, thin film at the workpiece surface. A common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction. CVD processes are routinely employed in many stages of manufacturing microelectronic components.
Atomic layer deposition (ALD) is another thin film deposition technique that is gaining prominence in manufacturing microfeatures on workpieces. FIGS. 1A and 1B schematically illustrate the basic operation of ALD processes. Referring to FIG. 1A, a layer of gas molecules A coats the surface of a workpiece W. The layer of A molecules is formed by exposing the workpiece W to a precursor gas containing A molecules and then purging the chamber with a purge gas to remove excess A molecules. This process can form a monolayer of A molecules on the surface of the workpiece W because the A molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. The layer of A molecules is then exposed to another precursor gas containing B molecules. The A molecules react with the B molecules to form an extremely thin layer of solid material C on the workpiece W. Such thin layers are referred to herein as nanolayers because they are typically less than 1 nm and usually less than 2 Å. For example, each cycle may form a layer having a thickness of approximately 0.5-1 Å. The chamber is then purged again with a purge gas to remove excess B molecules.
Another type of CVD process is plasma CVD in which energy is added to the gases inside the reaction chamber to form a plasma. U.S. Pat. No. 6,347,602 discloses several types of plasma CVD reactors. FIG. 2 schematically illustrates a conventional plasma processing system including a processing vessel 2 including a microwave transmitting window 4. The plasma processing system further includes a microwave generator 6 having a rectangular wave guide 8 and a disk-shaped antenna 10. The microwaves radiated by the antenna 10 propagate through the window 4 and into the processing vessel 2. The processing system 10 further includes a gas distributor 12 having an annular chamber 14 and a plurality of openings 16 facing radially inwardly into the processing vessel 2. The annular chamber 14 of the gas distributor 12 is not open to the window 4 such that the microwaves do not enter the chamber 14. In operation, a gas G flows radially inwardly through the openings 16 as the microwaves pass through the window 4 to form a plasma by electron cyclotron resonance. The plasma can be used to deposit or etch material on the workpiece W.
Although plasma CVD processes are useful for several applications, such as gate hardening, they may produce non-uniform films or features on a workpiece. For example, the plasma is concentrated in peripheral zones P1 and P2 near the openings 16 of the gas distributor 12. The central region of the processing vessel 2 along the center line CL accordingly has less plasma than the peripheral zones P1 and P2. The non-uniform concentration of the plasma proximate to the gas distributor 12 typically results in a non-uniform coating or non-uniform etching across the workpiece W. Such non-uniformities limit the utility of plasma vapor processing for forming very small microfeatures. Therefore, plasma vapor processing for depositing or etching materials on workpieces W may introduce unacceptable non-uniformities in many current microfeature devices.